Electric semiconductor devices



Nov. 17, 1959 J. A. LENO ELECTRIC SEMICONDUCTOR DEVICES 2 Sheets-Shet Filed Feb. 16, 1955 Inventor J. A. L. EN-O y Nov. 17, 1959 J. A. LENQ 2,913,643

7 v ELECTRIC SEMICONDUCTOR DEVICES Filed Feb. 16, 1955 '2 Sheets-Sheet 2 Inventor J. ALENO Attorney e V 2,913,64s a ELECTRIC SEMICONDUCTOR DEVICES John Albert L'eno, London, England, 'assignorto Interna- United States Patent tional Standard Electric Corporation, New York, N .Y.,

a corporation of Delaware Application February 16, 1955, Serial No. 488,561 Claims priority, application Great Britain March 25, 1954 9 Claims. c1. sir-#235 Thepresent invention relates to the construction of electric semi-conductor devices, and concerns more particularly devices such as crystalatriodes of the kind which two 'fine wire electrodes or catswhiskers are placed in contact with the surface of a semi-conducting crystal, such as germanium. t

In the case of crystal triodes, the points of the catswhiskers have usually to be placed very close together, and in order to obtain reproducible characteristics for the device, the spacing and pressure of the electrodes has to be carefully controlled.

The principalobject of the present invention is to provide a construction for a crystal triode or similar device having at least two catswhisk'er electrodes, which will allow the required spacing to be conveniently and accurately obtained.-

This object is achieved according to the invention by a slice of semi-conducting material having a plurality of sharplyjpointed fine wire electrodes or catswhiskers making contact with oneface of the slice, the spacing of the points of two of the said electrodes being determined by a thin membrane orsheet of insulating material, arranged therebetween, and arranged perpendicu larly in contact with the said face, the ends of the said electrodes being inclined'to the said membrane or sheet or a ceramic material. The body 1 is fused or otherwis fixed into an annular metal ring 2 in the form of a channel. The body 1, also carries three metal sleeves 3, 4 and 5, which are fused or moulded into the body. The central sleeve 4, is expanded into conical form at the upper end 6 and accommodates a metal rod 7, having a flat head8, surrounded by a metal tube 9. The arrangement of the elements 7,8 and 9 is shown more clearly in Figs. 3 and"4.

Between the lower part of the rod 7 and the head 8 is a conical portion 11, whichfits the conical upper end 6 of sleeve 4, shown'in Fig. 2. On the upper surface of the head 8, there is fixed by soldering or otherwisea slice 10 of semi-conductingmaterial, such asgermanium, and, resting symmetrically on, an d perpendicularly to this slice, isa thin sheet or membrane 12 held in diametricallyppposite. slots'of the tube ;9. The sheet 12 may,

for example, be made'of mica or glass.

The semi-conducting. slice, 10 is fi-xed to the head 8 of the rod 7, with a suitable soldering alloy, and the assembly is then placed in a suitable jig and lapped down to-the required thickness which m y, for example, be from 0.005" to 0.0307, according to the performance desired. The lapped face is then cleaned and etched to produce a suitable surface, after which the head 8 of the rod .7 is fixed with a drive fit into the metal tube 9. Thesheet or membrane 12 is next fitted into the slots of the tube ;9 and secured with a suitable adhesive. thickness to be chosen for the membrane 12 will depend upon the characteristics required for the crystal triode.

I; Fori example, if the crystal triode is required to operate providing an electric semi-conductor device comprising second, a suitable thickness would-beabout 0.002.

in such manner that substantially only the pointof each electrode makes contactwith the membrane or, sheet.

The invention is concernedwith a convenient form of construction for crystal triodes andsimilar devices, to which the principles described in the specification accompany the applicationof C. F. Drake for Metal Semi- Conductor, Serial No. 457,747,filed September 22, 1954-,

will be applied. Accordingly, in the present specification, fulldetails of such matters as electro-forming, contact pressure, and methods of electrolytic pointing of catswhiskers are not given.

The invention will be described with reference to the accompanying drawings, in which:

Fig. 1 shows a top view. of a crystal triode according to the invention; "Fig. 2 shows a partly sectioned side elevation of the crystal triode shown in Fig. l;-

Fig.3 shows a top view of one of the parts of the crystal triode shown in Figs. 1 and 2;

Fig. 4 shows a sectional view .at the line XX of Fig. 3; c

Fig.5 shows a side view'of a catswhisker assembly used in the crystal triodefshown in Figs. 1 and 2;

Fig. 6 shows a top View of, the'catswhisker assembly shown in Fig. 5. c i f i Fig. 7 shows a top view of an alternative form of the crystal triode; and V Fig. 8 shows a sectional view of Fig. 7, taken at the line Y--Y.' I

Reference will first be j-made to Figs. l

and 2. The

. The completed sub-assembly shown in Figs. 3 and 4 is nowfittedinto the sleeve 4 (Fig. 2) and tightly pressed home, sotha'tthe; conical surface of the portion 11; comes closely into contact withithe conical mouth 6 of the sleeve 4. The lower end of the rod 7 is soldered at 13 tq'the, sleeve 4, thus making an assembly which isrigid infs'pitelof differences betweenEthe diameters of the rod 7 and jsjleevef il' i V Q 'Ihef crystal triode, is now/provided with; two similar catswhisker assemblies, shown in Figs. 5 and 6. Each catswhisker assembly comprisesa'metalrod 14, having a circular hole'drilled at the upper end to accommodate the catswhisker electrode l5, which is made from a fine carefully straightened wire. This wire is fitted into thehole at thefupper end o'f thefrod 14, andis secured by swaging the upperrendbetween V-shaped dies, thus giv ing. it' a squ are section. In this way, the catswhisker wire isfirmly bonded into the rod 14.

The wire is then bent into the form shown in Fig. 5 and comprises a portion 16 at right-angles toitheaxis of the rod 13 and inclined portion 17. which makes an angle of 80 with the portion 16 as shown, The of the portion 17 is cut oifat 'an angle of 25 with the axis of the portion 17, thus forming .'a chisel point. The, point :so' produced shouldibe as sharp as possible, and

should be further sharpened by a suitable electrolytic proc'e ss which is operated under carefully controlled conditions. The process used, may, for example, ,be that described in the specification of'application, Serial No.-

. 457,747, mentioned above.

crystal triode is mounted on a' body 1, made of some,

suitable high stability insulating material, such as glass,

iThe diameter of the wire forming the meterialsmay be -usd for thiswire: for example, platiquantitiesc'f suitable significant impurities according to catswhisker maypfdr example, be of the order, of 0.005". Various the characteristicsdesired for the crystal triode. ,In the 7 I case-of a crystal triodeintended for use at high frequencies, satisfactory results have been obtained by using platinum-ruthenium for the emitter electrode and Phosphor-bronze forthe collector electrode;

The two cats-whisker assemblies designed as described with reference to Figs. 5' and 6 are inserted into the tubes -3' and 5' shown in Fig. 2 in such mannerthat the points of the two cats-whiskers come on opposite sides ofthe membrane 12. The rods 14 and'1'8 should be spaced from the rod 7 in such mannerthat the ends of the catswhiskers will be pressed lightly against'the membrane 12 when the rods are sliding in their corresponding sleeves. The assembly is located in a suitable jig (not shown), by means of which the rods 14- and- 18- of the electrode assemblies can be adjusted-vertically-by means ofmicrometer screws. Care should be taken'that the points of the catswhiskers areaccurately opposite to one another on either side ofthe membrane 12. Each rod is then carefully lowered by'means of the corresponding micrometer screw until the catswhisker' makes contact with the surface of the crystal slice 10. Contact can be detected by arranging so that an electric circuit (not shown) containingan indicatinginstrumentis completed when contactis made. The rod corresponding to, the collector electrode is then adjustedin such manner that the point of the corresponding catswhisker presses upon the surface of the crystal with a force of about 0.2 gram. The rod corresponding to the emitter electrode, is adjusted so that the catswhisker point presses upon the crystal surface with a force of 1.2 grams.

The contacts of the catswhiskers are now; subjected to a suitable electro-forming process, according to the characteristics required for the crystal triode. Electro-forming processes are described for example in the specification of application, Serial No. 457,747 already. referred to. The particular process to be used will depend on the characteristics required for the crystal triode.

After the completion of the electro-forming process, the force exerted by the collector electrode on the crystal is increased by about 0.4 gram, and that exerted by the emitter electrode by about 6 grams- The rods 14 and, 18 are then secured in position by soldering preferably at both ends, as indicated at .19 and 20.

Theamount of longitudinal adjustment of the'rods 14 and 18 necessary to produce the required force pressing on the crystal surface will, of course, depend upon the mechanical properties of the wire of which the catswhisker are composed. When the material of" this wire has been chosen, it is possible to calculate from the form of the wire, as shown in Fig. 5, the amount of movement of the rod which will produce a given force pressing on thesurface'.

In some cases, it may be desirable to protect the contacts by the use of some suitable organic insulating compound or wax with which the tube 9 may be, filledl The complete assembly is enclosed in a cylindrical metal cover 21, shown in Fig.2, which fits the annular channel of the ring 2,.as shown, and'which may be secured therein, for example by. soldering.

' A slightly different arrangement is shown in-Figs. 7. and 8. In this case, the main body ofthe' device consists of a circular disc offinsulating material 22, having a central; recess 23, which accommodates thehead 24-of a rod 25 which fits 'into asleeve 26, moulded into. the body 22. The crystal slice 27' is mounted on the head 24, in the manner already described.- Two. sheets or membranes 28 and 29 are securedat right angles. in slots.in

the body-22, as shown, and rest perpendicularly on the crystal slice 27. Two catswhisker assemblies, similar to that shown, in Figs. 5 and 6, are arranged, in sleeves- 30 and 31, moulded into the body '22. in suchmanner that the points of the catswhiskers'make conta,ct,.with the crystal in: two oppositecorners' betweenthe, two. sheets, a's-shown in Fig. 7, The thickness ofv these sheets is so chosen that the points of the cats-whiskers will be separated by the required amount when arranged in this way. The adjustment of the contact pressures may be carried out in the manner described with reference to Figs. 1 and 2. If desired, the recess 23 may be filled with a suitable insulating compound, and a cover (not shown), similar to 21 shown in Fig. 1, may be secured in some suitable way to the body 22. I

It will be obvious that, if desired, additional catswhiskers (not shown) could beplaced in either or both of the remaining corners between the membranes 28 and 29.

It should bepointed out that the use of an insulating sheet or membrane'for separating two of the catswhiskers of a crystal triode or similar'device has already been suggested. An example can be found, for instance, in US. application, Serial No. 174,693, filed July 19, 1950. In this case, however, while the. membraneacts efficiently to prevent the electrodes from coming into contact, it does not necessarily provide a very accurate spacing between the points of the two electrodes.

This accuracy of spacing is obtained, according to the present invention, by shaping the end of the catswhisker, as shown in Fig, 5, so that it will be inclined to the membrane, whereby contact with the membrane occurs substantially only at the point. of the catswhisker. Thus, when, the radius at the point: of the catswhisker is accurately determined by the electrolytic pointing process employed, the spacing between the points of contact of the two catswhiskers with the crystal surface on either side of the membrane will also be accurately determined.

Although germanium will generally be used as the semi-conducting material, the invention is not restricted to crystal triodes employing germanium; for example, siiicon could be used instead of germanium.

' Reference has been made above to the addition of small quantitiesof significant impurities to thematerial of a. catswhisker. Such impurities may, for example, be phosphorus, arsenic, antimony, aluminium,.indium or gold or mixtures of some of these. a

' While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is. to be clearly understood that this description ismade only by way of example and not as a limitation on the scope of the invention. i I

What I claim is:

1. An electric, semi-conducting device comprising a slice of semi-conducting" material-, a plurality of sharply pointed fine wire electrodes. positioned adjacent said 'slice with the points of said. electrodes making contact with one, face of said slice, two. intersecting sheets of insulating material, each mounted between twoof said electrodes perpendicular to and in contact withsaid face, the wire electrodes being inclined to, said sheets with only the point of. each electrode bearing against said sheets at an angle thereto and meansn for urging said electrodes against saidface in a normaldirection thereto, whereby said sheets determine'the spacing of the points of said electrodes.

2. An electric semi-conducting device comprising a slice of semi-conducting materiah-a plurality of sharply pointed fine wire electrodes positioned adjacent said; slice with the points of said electrodes'makingcontact with one face of said-slice, athin sheet "of insulating 'material mounted-between two of said electrodes, perpendicuiar to said face, and in contact with said face, the wire electrodes being inclined to-said sheet'with only the point of each electrode bearing against saidlsheet at an angle thereto, means for urgingisaid electrodes against said. face in a normal direction thereto whereby. said sheet determines the spacing of the points of said electrodes, a supporting body of; insulating material, a first metal rod secured in said body, the'slice offsemi-conducting material being mounted on the end thereof, additional metal rods each having one of the fine wire electrodes mounted on the end thereof, and elongated guide means secured in said body parallel to said first rod for supporting said additional rods parallel to said first rod and permitting longitudinal adjustment thereof prior to securing said additional rods to said guide means.

3. A device, according to claim 2, in which the first rod is provided with an cnlarged 'head on which the said slice is mounted, further comprising a metal tube attached to said head and enclosing said slice and the ends of the fine wire electrodes. 3

4. A device, according to claim 3 in which the said metal tube is filled with a protective insulating compound.

5. A device, according to claim 2, further comprising a metal cover secured to the body and enclosing the slice of semi-conducting material and the electrodes.

6. A device, according to claim 3, in which the metal tube is provided with diametrically positioned slots parallel to the axis of said tube for receiving and securing it in perpendicular relation to the surface of the slice.

7. A device according to claim 2, further comprising an elongated sleeve secured in the support for supporting the first rod, said sleeve having a conical enlargement at the end thereof, said first rod having an enlarged head on which the slice is mounted and a conical portion between said head and the rod proper which engages said conical enlargement of said sleeve when said rod is pushed into said sleeve, whereby said rod may be accurately centered therein.

8. A device, according to claim 2, in which each fine wire electrode has a first portion extending substantially at right angles to its supporting rod and an end portion bent towards said supporting rod at an angle of substantially with respect to said first portion, and the point is bevelled at substantially 25 with respect to said end portion and away from said supporting rod.

9. The method of manufacturing an electric semi-conducting device having a slice of semi-conducting material mounted on a support and at least two fine wire electrodes also mounted on the support with the pointed ends thereof in spaced point contact with a face of said slice which comprises adjusting each electrode in a direction normal to said face until the point thereof exerts a predetermined force on said face, subjecting said contacts of said electrodes and face to electro-forming treatment, further adjusting each electrode in a di rection normal to said face to produce a given increase of said force exerted on said face, and securing each electrode in adjusted position to said support.

References Cited in the file of this patent UNITED STATES PATENTS 2,661,448 Rogers Dec. 1, 1953 2,664,528 Stelmak Dec. 29, 1953 2,666,873 Slade Jan. 19, 1954 2,673,311 Amico Mar. 23, 1954 2,696,575 Fogg Dec. 7, 1954 2,717,341 North Sept. 6, 1955 

